The present invention relates to diamond tools. More particularly, the present invention relates to a method of brazing diamond abrasive particles to a substrate to make a monolayer diamond abrasive or cutting tool. The present invention facilitates control of the strength with which abrasive particles are held by the bonding agent.
There are various methods of making diamond abrasive or cutting tools. The present invention is concerned with monolayer diamond abrasive tools which are tools having only a single layer of diamond abrasive particles on the tool substrate. Monolayer diamond abrasive tools encounter difficulties in regard to attaching the individual diamond abrasive particles to the tool substrate or core. This is especially the case where a brazing or soldering technique is employed.
A variety of bonding methods have heretofore been used for bonding diamond or other carbon containing abrasives by brazing or soldering. At the present time, known brazing alloys for diamond abrasive materials include alloys based on copper, silver or gold doped with additives of iron, cobalt and nickel taken either separately or in combination with one another.
Also known are brazing alloys such as, copper-titanium, silver titanium, gold titanium, tin titanium, lead-titanium, copper-molybdenum, copper zirconium, copper vanadium, gold-tantalum, gold-niobium, copper-silver-titanium, copper-gold titanium, bronze-titanium and copper-tin-titanium. The content of Ti, Mo, Zr and V in such alloys generally amounts up to 10 weight percent, see for examples, "Wetting and Interaction of Metal Melts with Surface of Diamond and Graphite", Yu. V. Naidich and G. A. Kolesuichenko, "Naukova dumku" Publishers, Kiev 1967 (in Russian).
Another brazing alloy known for use with diamond is essentially an alloy of gold with 1-25 weight percent of tantalum, U.S. Pat. No. 3,192,620. This alloy, however, has a high liquid-phase point (above 1050.degree. C.) and therefore is restricted but to a narrow field of application, since at 1050.degree. C. and over diamond is liable to vigorously pass into a hexagonal form of carbon which adversely affects the strength of the abrasive.
Another diamond brazing alloy now in common use, consists of 75 weight percent copper and 25 weight percent of titanium.
A disadvantage of this alloy is that it is brittle and its thermal expansion factor differs substantially from that of the diamond. These properties lead to thermal stresses in finished products which, in turn, lead to rapid failure in the course of operation and consequently, high and premature wear of the tool made of such abrasives.
All of the brazing alloys described above are used also for metallization of abrasives made of diamond, cubic boron nitride, corundum, etc. Apart from the alloys discussed above, there are also known some alloys and single metals for surface metallization of abrasive, Viz., diamond, cubic boron nitride, silicon carbide, and tungsten carbide, the metallization being either single or multiple-layer. For establishing the initial layer, use is made of nickel, copper, zinc, tin, gold, lead or their alloys; if a second layer is desired, iron-nickel alloy is used or the like. For the third layer, copper or bronze is commonly used.
The coated crystals are then used to make polycrystalline diamond compacts as are commonly used in sintered metal bonded abrasive and cutting tools.
It is known in the art to metallize diamond and abrasives using alloys of silver-gold-titanium-cobalt-tantalum, copper-tin-tungsten and/or molybdenum-tantalum-nickel and/or cobalt-lead and/or bismuth-titanium and/or zirconium. Alloys used for brazing feature the use of an alloy of copper-tin-tungsten, molybdenum-tantalum-titanium and/or zirconium-cobalt and/or nickel-lead and/or bismuth, see for example, U.S. Pat. No. 4,009,027).
Yet another known brazing alloy contains nickel and/or cobalt-chromium-boron and/or silicon and/or phosphorous, see for example, U.S. Pat. No. 4,018,576). Chromium is claimed to wet the surface of the diamond causing tenacious adhesion of the diamond to the braze.
One common disadvantage of the above methods is that they are limited in the scope of their ability to vary the strength with which the braze bonds to the diamond. Another disadvantage of some methods is their use of costly precious metals and vacuums of 10.sup.-5 torr. Even the use of metals such as copper is not economical as they cannot be processed without the use of a high vacuum or expensive dry hydrogen furnaces so as not to form hydrides of the active metals.
Furthermore, most processes in the art heretofore required that two separate costly operations be performed; first coating the abrasive by metallizing or the like and then applying a braze in an additional operation.
There remains a need, however, for an improved low cost practical method of brazing a monolayer of diamond particles to a tool substrate. In accordance with the present invention, an improved method of forming a brazed monolayer of diamond particles is provided which is simpler and more effective than these prior methods. In the present invention, a carbide forming substance including a carbide forming element is mixed with a braze material in a temporary binder. This coating is coated onto the tool substance and a layer of diamonds is applied thereover. The resultant tool is heated to an effective temperature for allowing the carbide forming substance to form an initial element carbide layer on the surface of the diamond after which the braze may readily attach to the carbide layer to securely hold the diamond to the tool substrate. The method of the present invention also has the advantage that the carbide and braze layers tend to climb up the side of the diamond particle as the heating step progresses, thereby allowing for increased strength in the final brazed tool. Additionally, the bond strength can be varied by varying the amount of carbide forming material used in the initial mixture utilized and the processing time which controls the climb of the carbide formation in the present invention.
Additional benefits and advantages of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.